On the Computation of EXIT Characteristics for Symbol-Based Iterative Decoding

In this contribution the authors propose an efficient method for computing symbol-based EXtrinsic Information Transfer (EXIT) charts, which are useful for estimating the convergence properties of non-binary iterative decoding. A standard solution is to apply a priori reliability information to the A Posteriori Probability (APP) constituent decoder and compute the resultant average extrinsic information at the decoder's output using multidimensional histogram measurements. However, the employment of this technique is only feasible for a low number of bits per symbol, since the complexity of this approach increases exponentially with the number of bits per symbol. They demonstrate that by averaging over a function of the extrinsic APPs for a long block the extrinsic information can be estimated at a low complexity.